Any help would be appreciated here. I have an 2005 YFZ, LTE, K&N and outerwear. The accelerates to about mid range then stumbles no matter what gear it is in. I am trying to re-jet, Used LTE's didn't come with jet kit, currently running stock needle in stock position, with a 172 main jet and a 48 pilot, 2 1/2 turns out on mixture screw. I have switched main jets changed needle position and nothing changes. Any clue on to what my problem is? C'mon guys come through for me.

 

try 5th clip on stock needle

 

I have the same problem with my yfz and thru HOURS of talking to other yfz owners and even speakin to dirt bike guys with the same 450 motor, this was the solution to the "SHUTTER, STUMBLING, HESITATION problem.........Boysen QuickShot Accelerator Pump Cover.
I have not done mine yet so i can't say YES this is the solution BUT the people that i've spoken with SWEAR by this product for this problem. Good luck and i hope this helps you.......[img]i/expressions/face-icon-small-smile.gif[/img]

 

 

Still learning how to handle the forums sorry, but let me know it you do it and it works big daddy.